Ouroboros

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Cardano

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Most blockchains make leader selection visible to everyone on the network. Cardano does the opposite. At every slot, each stake pool runs a private lottery that only it can see, and the result determines whether that pool gets to produce the next block.
<h2 id="how-the-private-lottery-works">How the Private Lottery Works</h2>
The mechanism behind this is a verifiable random function (VRF). <cite>VRFs allow pools to run a lottery locally and privately using a secret key. If the resulting number falls below a certain threshold, that pool is elected slot leader.</cite><cite>The threshold is calculated so that the higher a pool's stake, the higher its probability of winning the slot.</cite>
The privacy is intentional and serves a security purpose: because no outsider can observe the draw in advance, attackers cannot identify and target upcoming block producers. Some slots produce no winner at all; occasionally two pools win simultaneously, and the protocol handles both outcomes by design. <cite>Short forks happen when two leaders produce blocks close together, known as slot battles, and nodes keep the valid chain with more blocks or density.</cite>
<cite>If a pool wins, it includes a proof in the block so everyone can verify the win after the fact.</cite><cite>In Praos, each epoch has an agreed-upon nonce that all participants must use as input to their VRF.</cite> That nonce is derived by hashing values from the blocks of the previous epoch, which is the loop encoded in the name Ouroboros, the ancient symbol of a snake eating its own tail.
<cite>Ouroboros is the first provably secure proof-of-stake protocol, and the first blockchain protocol to be based on peer-reviewed research.</cite><cite>In the Cardano protocol, time is divided into epochs that last 432,000 slots, each lasting one second.</cite>
<h2 id="delegation-staking-rights-without-giving-up-your-coins">Delegation: Staking Rights Without Giving Up Your Coins</h2>
Delegating <a href="https://x.com/search?q=%24ADA&amp;src=cashtag_click" rel="noopener noreferrer nofollow">$ADA</a> to a pool on <a href="https://x.com/Cardano" rel="noopener noreferrer nofollow">@Cardano</a> assigns participation rights only. <cite>Cardano's delegation is non-custodial: your ADA never leaves your wallet. You issue an on-chain certificate that counts your stake toward a pool while keeping full spending control.</cite> Any ADA spent simply drops out of the stake count for that epoch.
<cite>There is no lock-up and no slashing. Delegated ADA is never at risk.</cite><cite>The more ADA a validator controls, either their own or delegated from others, the higher the probability of being chosen to create a block and receive rewards.</cite>
The combination of a private VRF lottery and non-custodial delegation gives Cardano's consensus model two distinctive properties: a meaningful security layer against targeted attacks, and a staking experience that keeps holders in full control of their funds at all times.
Sources: <a href="https://cardano.org/ouroboros/" rel="noopener noreferrer nofollow">Cardano.org: Ouroboros Proof-of-Stake Protocol</a> <a href="https://cardanofoundation.org/blog/introduction-proof-of-stake-blockchains" rel="noopener noreferrer nofollow">Cardano Foundation: Introduction to Proof of Stake Blockchains</a> <a href="https://developers.cardano.org/docs/developers/curriculum/staking-governance/staking/" rel="noopener noreferrer nofollow">Cardano Developer Portal: Staking and Delegation</a>

Cardano picks its block producers through a lottery only the winner can see

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